Viscoelastic Surfactants with High Salt Tolerance,Fast‐Dissolving Property,and Ultralow Interfacial Tension for Chemical Flooding in Offshore Oilfields

Injected chemical flooding systems with high salinity tolerance and fast‐dissolving performance are specially required for enhancing oil recovery in offshore oilfields. In this work, a new type of viscoelastic‐surfactant (VES) solution, which meets these criteria, was prepared by simply mixing the zwitterionic surfactant N‐hexadecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (HDPS) or N‐octyldecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (ODPS) with anionic surfactants such as sodium dodecyl sulfate (SDS). Various properties of the surfactant system, including viscoelasticity, dissolution properties, reduction of oil/water interfacial tension (IFT), and oil‐displacement efficiency of the mixed surfactant system, have been studied systematically. A rheology study proves that at high salinity, 0.73 wt.% HDPS/SDS‐ and 0.39 wt.% ODPS/SDS‐mixed surfactant systems formed worm‐like micelles with viscosity reaching 42.3 and 23.8 mPa s at a shear rate of 6 s^?1, respectively. Additionally, the HDPS/SDS and ODPS/SDS surfactant mixtures also exhibit a fast‐dissolving property (dissolution time <25 min) in brine. More importantly, those surfactant mixtures can significantly reduce the IFT of oil–water interfaces. As an example, the minimum of dynamic‐IFT (IFT_min) could reach 1.17 × 10^?2 mN m^?1 between the Bohai Oilfield crude oil and 0.39 wt.% ODPS/SDS solution. Another interesting finding is that polyelectrolytes such as sodium of polyepoxysuccinic acid can be used as a regulator for adjusting IFT_min to an ultralow level (<10^?2 mN m^?1). Taking advantage of the mobility control and reducing the oil/water IFT of those surfactant mixtures, the VES flooding demonstrates excellent oil‐displacement efficiency, which is close to that of polymer/surfactant flooding or polymer/surfactant/alkali flooding. Our work provides a new type of VES flooding system with excellent performances for chemical flooding in offshore oilfields.     

压裂酸化用粘弹性表面活性剂溶液研究进展

粘弹性表面活性剂溶液的高表面活性及独特的流变特性可以作为理想的压裂、酸化、砾石充填等增产改造以及三次采油措施流体。详细介绍了粘弹性表面活性剂流体的组成、制备与表征方法,阐述了典型粘弹性表面活性剂流体流变特性研究现状;概述了粘弹性表面活性剂流体在压裂、酸化等增产措施中的应用进展,并指出了粘弹性表面活性剂流体矿场推广应用尚需解决的问题。     

Application of pH-Responsive Viscoelastic Surfactant as Recyclable Fluid at High Temperature

A pH-responsive amphiphilic surfactant stearic amide 3-(N,N-dimethylamino)propylamide (SAA) was synthesized and served as a thickener in aqueous solution to construct a switchable viscoelastic surfactant fluid (VES fluid). The structure of SAA was studied by ¹H NMR, and the viscoelastic behavior of VES fluid was studied in detail by rheological measurements. The viscosity of this VES fluid can be switched reversibly from low to high immediately by adjusting system pH value. Even at high shear rate (170 s⁻¹) and high temperature (90 °C), excellent viscoelastic behavior of this VES fluid can be observed, which is a key performance for fracturing applications. Meanwhile, the recycled VES fluid can still maintain good pH-responsive behavior even after more than three cycles. These unique performances of this VES fluid not only enhanced our understanding of the transformation of wormlike micelles at high temperature, but also enriched a large potential of VES fracturing fluid in the development of oil and gas reservoirs.     

乳化方式及助乳化剂对蓖麻油乳化液性能的影响

分别采用恒速搅拌乳化、高剪切乳化及超声波乳化3种方式,以非离子型表面活性剂失水山梨醇单脂肪酸酯(Span)与聚氧乙烯失水山梨醇单脂肪酸酯(Tween)为复合乳化剂对蓖麻油进行乳化,考察了助乳化剂正辛醇、异辛醇、十二醇对乳化体系稳定性的影响。结果表明,随助乳化剂脂肪醇碳链长度的增加,蓖麻油的乳化稳定性提高;采用超声波乳化方式可制得稳定的蓖麻油乳化液,且稀释稳定性良好。     

Synthesis and characterization of multi‐hollow opaque polymer pigments

A new generation multihollow opaque polymer pigment was synthesized by suspension polymerization of “water‐in‐oil‐in‐water” emulsion method, where methyl methacrylate and ethylene glycol dimethacrylate monomer mixture was used as oil phase. The effects of surfactant and cosurfactant composition in terms of “hydrophilic/lipophilic balance” on the stability of the “water‐in‐oil” emulsion and the size of water droplets were studied. Low droplet sizes and the optimum stability were obtained with “Span 80&Tween 80” surfactant mixture at an HLB value of 8. The desired size distribution was obtained at “monomer/surfactant/water” ratio of 75.5/9.4/15.1 at an ultrasonic mixing power of 80 W lasting for 30 s. The surface morphology and hollow structure of polymer pigments were analyzed by scanning and transmission electron microscopy techniques. L*a*b color and gloss properties of polymer pigments were examined. The opacity values were assessed by contrast ratio measurements, and the pigments provided up to 97.3% opacity with 50% v/v solid content in resin. In addition, the pigments exhibited low gloss values and yielded matte films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43696.     

Viscoelastic characterization of semiconducting dodecylbenzenesulfonic acid doped polyaniline electrorheological suspensions

Dodecylbenzenesulfonic acid (DBSA)‐doped polyaniline particles were synthesized via emulsion polymerization, and electrorheological (ER) fluids were prepared by dispersing the synthesized polyaniline particles in silicone oil. The viscoelastic properties of DBSA‐doped polyaniline/silicone oil ER systems were examined using a vertical oscillation rheometer (VOR), which is designed for the rheological measurement of ER fluids, with a high voltage generator. Viscoelastic data obtained from the VOR were compared with those obtained from a commercial Physica rotational rheometer. The data from VOR were quite reliable in a broad range of both strain and frequency. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 108–114, 2001     

油酸钠蠕虫状胶束的性质及驱油效率研究

分别通过稳态、动态流变的方法和冷冻蚀刻透射电镜、室内模拟驱油实验和平板夹砂微观模型驱油实验,研究了由碳酸钠诱导形成的油酸钠蠕虫状胶束的流变学性质及形貌和蠕虫状胶束驱油配方的驱油效果及驱油微观机理。结果表明,在油酸钠(NaOA)溶液中,加入一定量的Na2CO3能够形成蠕虫状胶束;孤岛东区稠油注聚驱后,蠕虫状胶束驱油配方(w/%,1.83 NaOA 4.24 Na2CO3)的室内模拟驱油可提高采收率25%原始石油地质储量(OO IP);平板夹砂微观驱油模型显示蠕虫状胶束驱油体系进入模型中,能够使注聚后束缚残余油重新启动、变形,渐渐形成油墙向出口处运移,蠕虫状胶束驱油体系能够有效扩大波及体积,提高洗油效率,从而提高驱油效率。     

Viscoelastic surfactant fluids filtration in porous media: A pore-scale study

We investigated the flow of viscoelastic surfactant (VES) solutions, an important type of fracturing fluids for unconventional hydrocarbon recovery, through a diverging–converging microfluidic channel that mimics realistic unit in porous media. Newtonian fluid and viscoelastic hydrolyzed polyacrylamide (HPAM) solution were used as control groups. We vary Deborah numbers (De) up to 61.2, and found that the flow patterns of HPAM and VES solutions become very different once De ≥ 6.12. This is attributed to different generation mechanisms of viscoelasticity, thus different responses to extensional rates at pore-throats, for HPAM and VES solutions. It results in significantly smaller pressure drop of VES solutions through the microchannel compared to HPAM solution. It interprets higher filtration loss of VES solution than HPAM in core experiments and in field observations. The set-up can be generalized as a prototype to effectively evaluate the filtration of fracturing fluids.     

Hydrophobically associating acrylamide‐based copolymer for chemically enhanced oil recovery

A hydrophobically associating copolymer was prepared by free‐radical polymerization with acrylamide (AM), acrylic acid (AA), and N‐allyloctadec‐9‐enamide (NAE) as monomers. The structure was characterized by Fourier transform infrared spectroscopy, ¹H‐NMR, ¹³C‐NMR, and scanning electron microscopy. The rheological experiments indicated that the copolymer possessed superior properties compared with partially hydrolyzed polyacryamide. It was found that an AM/AA/NAE/Tween‐80 system could effectively decrease the interfacial tension and reduce the surfactant loss caused by stratum adsorption in polymer–surfactant flooding. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2901–2911, 2013     

Novel fluorinated surfactants for enhanced oil recovery in carbonate reservoirs

Novel surfactant‐polymer (SP) formulations containing fluorinated amphoteric surfactant (surfactant‐A) and fluorinated anionic surfactant (surfactant‐B) with partially hydrolyzed polyacrylamide (HPAM) were evaluated for enhanced oil recovery applications in carbonate reservoirs. Thermal stability, rheological properties, interfacial tension, and adsorption on the mineral surface were measured. The effects of the surfactant type, surfactant concentration, temperature, and salinity on the rheological properties of the SP systems were examined. Both surfactants were found to be thermally stable at a high temperature (90 °C). Surfactant‐B decreased the viscosity and the storage modulus of the HPAM. Surfactant‐A had no influence on the rheological properties of the HPAM. Surfactant‐A showed complete solubility and thermal stability in seawater at 90 °C. Only surfactant‐A was used in adsorption, interfacial tension, and core flooding experiments, since surfactant‐B was not completely soluble in seawater and therefore was limited to deionized water. A decrease in oil/water interfacial tension (IFT) of almost one order of magnitude was observed when adding surfactant‐A. However, betaine‐based co‐surfactant reduced the IFT to 10^?3 mN/m. An adsorption isotherm showed that the maximum adsorption of surfactant‐A was 1 mg per g of rock. Core flooding experiments showed 42 % additional oil recovery using 2.5 g/L (2500 ppm) HPAM and 0.001 g/g (0.1 mass%) amphoteric surfactant at 90 °C.     

硅酸盐复合黏弹性驱油剂的研究与评价

使用黏弹性表面活性剂形成具有一定黏弹性的蠕虫状胶束,所需原料的浓度较高,成本较高,制约了黏弹性表面活性剂驱油剂在现场的应用。以液体硅酸钠、两性表面活性剂、纳米二氧化硅为原料,制备了在经济使用浓度下能够显著提高注入水黏度且具有优良驱油性能的黏弹性驱油剂。透射电镜表征结果表明,驱油剂在有效质量分数为0.3%条件下即可达到较高的黏度。调整液体硅酸钠、表面活性剂的有效质量分数为0.12%~0.20%,制备的驱油剂的黏度达到10~50 mPa·s。实验对比了常用聚合物与黏弹性驱油剂的驱油效果,结果显示黏弹性驱油剂的驱油效果几乎是聚合物的2倍。这项工作为开发新型高效驱油剂提供了新方法,也为驱油剂流变学研究提供了新思路。     

Preparation of a salt-responsive Gemini viscoelastic surfactant for application to solids-free drilling fluids

In order to solve the problem of poor rheological properties of solid-free drilling fluids in salt-bearing formations and prevent drilling accidents such as lost circulation, formation collapse, and wellbore instability, it is crucial to develop a new type of viscosifier. In this study, a salt-responsive Gemini viscoelastic surfactant (NT-1) was synthesized by using erucamide as a hydrophobic chain and introducing a benzene ring and a carboxyl group into the linker. In addition, it is used as a viscosifier for solid-free drilling fluids. The structure of the surfactant was characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, Fourier transform infrared spectroscopy, and electrospray ionization tandem mass spectrometry (ESI-MS), and its physicochemical properties were determined by surface tensiometer, thermogravimetric-differential scanning calorimetry, dynamic lighting scattering and rheometer. Its performance in solid-free drilling fluids was evaluated according to the American Petroleum Institute (API) standard. The results show that the surfactant has a low critical micelle concentration (31.74 μmol/L), excellent thermal stability and water solubility. In particular, NT-1 can self-assemble into worm-like micelles under the action of salt, and the spatial network structure formed by the interweaving of these micelles can endow the drilling fluid with good rheology and viscoelasticity. NT-1 is compatible with conventional drilling fluid polymer additives, which can effectively improve solid-free drilling fluids' rheological properties and fluid loss properties in salt layers. The temperature resistance in drilling fluid systems can reach 120°C. This work verifies the feasibility of using viscoelastic surfactants as viscosifiers in solid-free drilling fluids and provides new ideas for developing salt-responsive smart drilling fluids.     

Rheological behavior of mixed system of ionic liquid [C8mim]Br and sodium oleate in water

We report on the rheological behavior of wormlike micelles constructed by ionic liquid surfactant [C₈mim]Br (1-octyl-3-methylimidazolium bromide) and anionic surfactant sodium oleate (NaOA) in aqueous solution. The effects of surfactant composition, total surfactant concentration, added salts, and temperature were investigated. The prevailing surfactant effect at lower concentration and the leading cosolvent effect at higher concentration of [C₈mim]Br may be the main reasons for appearance of well-established maximum in key rheological parameters with variation of surfactant composition and total surfactant concentration. The Cole-Cole plots demonstrate that the systems (total surfactant concentration falls within 0.17–0.35 mol·L^-1 and molar ratio 0.33≤R≤0.50) fit the Maxwell’s mechanical model as linear viscoelastic fluid. The addition of NaBr or sodium salicylate decreases significantly the viscosity and the relaxation time of the wormlike micelle solution but cannot change the value of plateau modulus G₀. The present system has low rheological tolerance to temperature. The increase of temperature decreases the average contour length and viscosity of wormlike micelles and thus strengthens the relaxation progress of diffusion and weakens the relaxation progress of reptation. Increasing the temperature also decreases the value of plateau modulus G₀ and shifts the minimum value of the loss modulus G^″_min to higher frequencies.     

Amphiphilic copolymers based on PEG‐acrylate as surface active water viscosifiers: Towards new potential systems for enhanced oil recovery

With the purpose of investigating new potential candidates for enhanced oil recovery (EOR), amphiphilic copolymers based on Poly(ethylene glycol) methyl ether acrylate (PEGA) have been prepared by Atom Transfer Radical Polymerization (ATRP). A P(PEGA) homopolymer, a block copolymer with styrene PS‐b‐P(PEGA), and an analogous terpolymer including also sodium methacrylate (MANa) in the poly(PEGA) (PPEGA) block, PS‐b‐P(PEGA‐co‐MANa) have been prepared and characterized. Viscosity and surface activity of solutions of the prepared polymers in pure and salty water have been measured and the results have been interpreted in terms of the chemical structures of the systems. A clear influence of the presence of the charged MANa moieties has been observed in both rheological and interfacial properties. The PS‐b‐P(PEGA‐co‐MANa) terpolymer, being an effective surface active viscosifying agent, is a good candidate as polymeric surfactant for applications in enhanced oil recovery and related. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44100.     

Performance optimization for the viscoelastic surfactant using nanoparticles for fracturing fluids

Abstract

In order to optimize the viscoelastic properties and temperature-resistance for the sodium 2,2'-(propane-1,3-diylbis(stearoylazanediyl))diethanesulfonate Gemini viscoelastic surfactant, the effects caused by the addition of nanoparticles were investigated. The viscous and rheological behaviors and microstructures of surfactant solutions with/without magnesium oxide (MgO) or lipophilic silicon dioxide (SiO₂) nanoparticles were studied using rheometer and field emission scanning microscopy electron microscopy (FESEM). The experimental results showed that the addition of optimal nanoparticle mass fractions significantly increases the viscoelastic properties for the viscoelastic micelle solutions at 90?°C. The enhancements in viscoelastic properties are ascribed to the formation of network structures due to the addition of nanoparticles. The use of nanoparticles showed promising improvements to be applied for fracturing fluids at high temperatures.     

微乳液组分对体系水增溶性能及钴蓝纳米颜料性能的影响

研究了Span80－Tween60／正己醇。120^＃汽油体系中各组分质量分数对微乳液水增溶性能的影响,其中：Span80为失水山梨醇单油酸酯;Tween60为聚氧乙烯失水山梨醇单硬脂酸酯。结果表明：Span80-Tween60复合表面活性剂中Span80质量分数为40%时,微乳液增溶水量达极大值。随复合表面活性剂含量的增加．微乳液增溶水量先增加后减少。随前驱液离子浓度的增加．微乳液增溶水量减少。微乳液各组分含量的改变导致微反应器性能的变化,并进一步影响所合成的CoAl2O4纳米颜料的性能。     

Effects of Rheological Behavior of Viscoelastic Surfactants on Formation Damage in Carbonate Rocks

Viscoelastic surfactants (VES) are used in various oilfield applications such as matrix stimulation and enhanced oil recovery. The loss of surfactants during the propagation of VES could result in a significant reduction in the permeability of the rock (formation damage). The objective of the current work was to identify the effect of rheological behavior of the VES on the formation damage using core‐flooding experiments, nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) analysis. A combination of core‐flooding, NMR, and SEM techniques was used to quantify and identify the location of formation damage in carbonate core samples. The viscosity and storage modulus strongly depend on the nature and concentration of salts. The viscosity increased by increasing the salt concentration up to a specific point (15 wt% CaCl₂) and then starts decreasing. The VES formulations that displayed the maximum and minimum viscosities were used to identify the impact of rheological behavior on formation damage. Core‐flooding experiments were performed to assess the formation damage due to high‐viscosity and low‐viscosity VES formulations. The reduction in the permeability of carbonate rocks reaches more than 90% of the initial permeability. It was found that low‐viscosity VES caused more damage compared with high‐viscosity VES when they were used at constant concentrations. NMR and core‐flooding results revealed that the damage took place both in pore body and pore throat. However, most of the surfactant was retained at the pore throat.     

Enzymatic activity of Chromobacterium viscosum lipase in an AOT/Tween 85 mixed reverse micellar system

To enhance the Chromobacterium viscosum lipase (glycerol‐ester hydrolase; EC 3.1.1.3) activity for the reaction of water‐insoluble substrates, the AOT/isooctane reverse micellar interface was modified by co‐adsorption of a non‐ionic surfactant. Polyoxyethylene sorbitan trioleate (Tween 85) was used as the non‐ionic surfactant and olive oil as a water‐insoluble substrate. An appreciable increase of lipase activity was observed and at higher W_o values (where W_o = molar ratio of water to total surfactants of the micellar system) there was no sharp fall of the enzyme activity such as a typical bell‐shaped profile. The kinetic model for the lipase‐catalysed hydrolysis of olive oil in AOT/isooctane reverse micellar system was applied to the enzymatic reaction in this mixed reverse micellar system. It was found that the predictions of the model agree well with the experimental kinetic results and that the adsorption equilibrium constant of olive oil molecules between the micellar phase and the bulk phase of the organic solvent is smaller in AOT/Tween 85 mixed reverse micellar systems than in simple AOT reverse micellar systems. © 1999 Society of Chemical Industry     

Preparation of SiO2/epoxy nanocomposite via reverse microemulsion in situ polymerization

Reverse water/oil (w/o) microemulsions composed of epoxy resin (EP) (the oil phase) and nonionic surfactant and ammonia aqueous solutions (the water phase) were used in the synthesis of SiO2/EP nanocomposites. The stability of reverse microemulsion was evaluated by measuring water solubilization of the microemulsion. Effects of surfactant type and content, ammonia concentration and temperature on the water solubilization were systematically investigated. Higher water solubilization capacity was obtained by nonionic surfactant TX‐100 compared with other two surfactants, Span‐80 and Tween‐80. Ammonia concentration of 5 wt% and preparation temperature at 35°C were favorable for forming a stable microemulsion and enabling the subsequent hydrolysis and condensation reaction of inorganic precursor tetraethoxysilane (TEOS). SiO2/ epoxy nanocomposites were prepared via in situ polymerization of TEOS within the nanoscale reverse microemulsion “water pool”. FTIR, SEM, and universal testing machine were used to characterize the structural and mechanical properties of the composite. The results revealed that the optimal mechanical properties were obtained at 3 wt% TEOS content. Compared with neat epoxy resin, the tensile and flexural strength of the composite were 40% and 12% higher, respectively. The formation of the silica structure in the hybrid was investigated with FTIR. The SEM and optical observations showed a ductile fracture morphology and good miscibility between inorganic and organic phases. POLYM. COMPOS., 35:1388–1394, 2014. © 2013 Society of Plastics Engineers     

黏弹性表面活性剂溶液中颗粒沉降特性研究

黏弹性表面活性剂溶液悬浮颗粒流广泛存在于自然界和工业生产中,黏弹性表面活性剂溶液的非线性流变性质及应力松弛效应对其中颗粒沉降有着显著影响。采用FENE-P和Giesekus黏弹性本构模型对表面活性剂溶液中颗粒沉降特性进行研究,发现两种本构模型不仅表现出剪切稀化,而且出现拉伸硬化。颗粒在沉降初期的不稳定性主要是由溶液自身的弹性效应引起,弹性效应越强,颗粒沉降速度不稳定性越强,而剪切稀化效应会减弱颗粒沉降速度的不稳定。颗粒沉降过程中在其尾部形成一个“负尾迹”,随着剪切稀化和拉伸硬化效应增强,负尾迹区增大,弹性效应增加,负尾迹增强,负尾迹区流体内部反向速度分布导致的表面活性剂溶液中微观胶束的拉伸断裂和重构可能是引起颗粒沉降速度持续波动的原因。